Embodiments relates to a real time location system (RTLS), and more particularly, to a PN synchronization or frame synchronization acquisition method of an RTLS.
Furthermore, embodiments relates to a method for dynamically acquiring a PN synchronization of a blink signal in a reader according to a channel state when a tag transmits a direct sequence spread spectrum (DSSS) blink signal having a predetermined period and the reader receives the blink signal in a 2.4 GHz RTLS system which complies with an ISO/IEC24730-2 standard, and a method for synchronizing a frame using a preamble.
In a RTLS system using a 2.4 GHz frequency band complying with an ISO/IEC24730-2 standard, an RTLS transmitter (or tag) periodically transmits a differentially encoded binary phase shift keying direction sequence spread spectrum (BPSK DSSS) signal including an RTLS transmitter ID into readers as a blink signal.
The plurality of readers disposed around the tag receive a transmitting signal of the tag to transmit the signal into a positioning engine of an RTLS server. The positioning engine of the RTLS server receives the transmitting signal of the tag from each of the readers to calculate a position of the tag through a time difference of arrival (TDOA) from the tag to each of the readers.
For example, when the tag is calculated in position on the basis of a TDOA read by two readers, a pair of hyperbolas may be defined by a difference of a distance measured using the readers as fixed points. Here, a point of intersection between the hyperbolas may be estimated as the position of the tag.
As described above, an ISO/IEC 24730-2 standard according to a related art may estimate a position of a tag using a TDOA of a transmitting signal of the tag received from a reader.
Here, in the ISO/IEC 24730-2 standard, a wireless transmitting channel is premised on a ling of sight (LOS), and a preamble is only 8 bits. However, in actual wireless communication channel environments, wireless signals may be attenuated, reflected, scattered, and refracted by an air temperature, a change of humidity, various obstructions, and the like.
If frequency synchronization within a short preamble of 9 bits, phase synchronization, PN synchronization and despreading, and data packet are not performed on a received signal affected by the unstable wireless transmitting channel, it may be difficult to decode data. Thus, a method in which synchronization is acquired even within a short preamble to decode desired date is required.
Also, to acquire PN synchronization in the other DSSS system according to a related art, a threshold valve of PN synchronization acquisition and a convergent range of PN synchronization tracking should be separately set according to each of channels and systems.